1. Field of the Invention
The present invention relates to an apparatus and a method for detecting a signal in a multi-antenna system. More particularly, the present invention relates to an apparatus and a method for detecting a signal with low complexity in a multi-antenna system using a spatial multiplexing scheme.
2. Description of the Related Art
Rapid growth of the wireless mobile communication market has created demand for various multimedia services in a radio environment. Many of the multimedia services require the transmission of a very large amount of data at a high data rate to provide the multimedia services. Accordingly, research is being conducted on a Multiple-Input Multiple-Output (MIMO) system which is able to transmit a large amount of data at a high data rate by the efficient utilization of limited frequencies.
Compared to a single-antenna system, the MIMO system can increase a channel transmission reliability and a data rate by transmitting data over independent channels per antenna, without the use of additional frequencies or an increase in transmission power.
When the MIMO system adopts a spatial multiplexing scheme, a transmitter can achieve a rapid data transmission by transmitting different information over multiple transmit antennas respectively. Via receive antennas, a receiver receives a signal including the transmitted signals having the different information from the transmit antennas. Accordingly, the receiver needs to separate the multiplexed signal on the basis of the antenna using a detection scheme. For example, the receiver may detect the multiplexed signal using a Zero-Forcing (ZF), a Minimum Mean Square Error (MMSE), an Order Successive Interference Cancellation (OSIC), and a Maximum Likelihood (ML) method. Alternatively, the receiver may adopt a suboptimal detection method such as sphere decoding, QR Decomposition-M, MOC, and QRD OSIC (QOC), to detect the multiplexed signal.
Using the ML estimation, the receiver selects a signal vector having a minimum square Euclidean distance to the receive signal among all the signal vectors transmittable from the transmitter. Thus, the receiver can achieve the optimum performance by means of the ML method. However, as the number of the transmit antennas and the modulation order increase, the computational complexity of the ML estimation increases as well.
Using the sphere decoding method, the receiver attains similar performance to the ML method. However, it is difficult to calculate a radius of the initial sphere and the computational complexity rises in a worst case.
Using the QRD-M method, the receiver is subject to severe performance variation depending on the number of candidate groups. If there are a large number of candidate groups, the receiver can obtain performance substantially similar to the ML method. However, the computational complexity rises.
Using the MOC or the QOC methods, the receiver obtains performance similar to the ML method with lower computation complexity than the QRD-M. Yet, as the number of the transmit antennas, receive antennas and modulation order increase, its computational complexity rises.
As discussed above, in detecting the multiplexed signals, the receiver is subject to high computational complexity in a MIMO system using the spatial multiplexing scheme. Therefore, an apparatus and method for achieving an optimum performance with lower computational complexity in a MIMO system using a spatial multiplexing scheme are needed.